ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

When creating the degenerated FE models, the angle between load and L4 vertebra was
kept constant. Scaling of the discs causes the angles between L3 and L4 as well as L4
and L5 to deviate slightly from the angles of the healthy model (Figure 1). Nevertheless,
the disc height decrease is mainly in the direction of the applied load. As a result, the
disc geometry changes cause no significant deviation of internal forces, stresses and
therefore strains in the cortical shell (Figure 1).
a) Healthy model (b) Mild degeneration (c) Full degeneration
Figure 1. FE models with different grades of degeneration
4. RESULTS
4.1 Validation of the FE model
Since it is impossible to experimentally mimic the spinal degeneration in a specimen,
the validation can only be performed for the healthy FE model which was achieved by
mechanically testing the healthy specimen.
Table 3. Comparison of FE prediction with experiment data
displacement [mm] discal pressure [MPa] principal strain []
U2 a U3 b L3-L4 L4-L5
max. min.
ventral lateral ventral lateral
Experiment -2.47 1.50 1.43 1.58 403.4 634.8 -441.6 -873.8
FEM -2.73 1.46 1.47 1.39 426.5 807.6 -439.9 -789.1
Deviation -10.6% 2.5% -2.7% 12.1% -5.1% -26.1% 0.3% 10.3%
a U2: vertical axis; b U3: anteroposterior axis
As there were some modifications of the previous developed FE model, the validation
was repeated in this study to ensure the appropriateness of the model. The healthy FE
model was exerted to a load of 2000N in the axial direction. The calculated results were
compared with the experimental measurement [18] (Table 3). The model predicted the